Submersible remote operated vehicle tool change control

ABSTRACT

A system receives data from a submersible remote operated vehicle (ROV), the data being about the operation of an arm of the ROV. The system automatically controls, based on the data, movement of the arm in docking the arm to a tool holder. In certain instances, the system implements an image based control. In certain instances, the system implements a force accommodation control. In certain instances, the system implements both.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/830,104, filed Apr. 5, 2019, the contents ofwhich are incorporated by reference herein.

BACKGROUND

In petrochemical exploration and production, many offshore wells are atdepths well beyond the reach of divers. In these instances, asubmersible remote operated vehicle (ROV) is controlled from above thewater's surface to perform some operations in the construction andcontrol of the wells. The ROV has a manipulator arm that can mount toolsfor use in performing these operations. Some manipulator arms have thecapability to remotely release from and attach to tools, so thatdifferent tools can be interchanged while the ROV is subsea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a submersible remote operated vehicle(ROV) operating subsea;

FIG. 2 is a perspective view of an example tool holder with a portion ofa docked manipulator arm;

FIG. 3A is a perspective view of a face plate of the tool holder of FIG.2 and FIG. 3B is a perspective view of the face plate with a male mountof a tool protruding through the faceplate;

FIG. 4 is a schematic of an aspect of the system described herein,including a control interface, sensors and actuators;

FIG. 5 is a flow diagram of steps in operation of automated docking ofthe manipulator arm to a tool holder;

FIG. 6 is a flow diagram of steps in operation of an image feedbackcontrol of the system; and

FIG. 7 is a flow diagram of steps in operation of a force accommodationcontrol of the system.

Throughout the figures, like reference numbers are used to indicate thelike parts.

DETAILED DESCRIPTION

FIG. 1 shows an example submersible remote operated vehicle (ROV) 10operating subsea. The ROV 10 can be controlled by a human operator froma control interface 12, typically on a vessel 30 (e.g., a platform, shipor other vessel) above a surface 14 of a body of water, to fly throughthe water and perform certain operations. The ROV 10 of FIG. 1 includesa manipulator arm 16 with a tool 18 attached to its end. In certaininstances, the ROV 10 can include one or more additional arms, such as agrabber or other type of arm, but the manipulator arm 16 is the mostdexterous, having multiple pivot and rotational joints 22 that enablemovement of the arm in multiple degrees of freedom. In certaininstances, the joints 22 in the manipulator arm 16 collectively provide6 degrees of freedom (i.e., movement along the X-axis, Y-axis, Z-axis,roll, pitch, and yaw). Each joint 22 includes a mechanical joint thatenables movement between the connected segments of the arm 16, one ormore actuators to drive movement of the joint and, in certain instances,one or more sensors, such as position and force (linear and/or torque)sensors.

The control interface 12 is communicably coupled to the ROV 10 submergedin the water. In some cases, the ROV 10 is connected to the controlinterface 12 through a tether management system (TMS) 24, also submergedin the water, and supported from the vessel 30. The operator controlsthe ROV 10 to fly around and perform operations and the TMS 24, inperforming those operations, via the control interface 12. An umbilical26 extends between the control interface 12 at the vessel 30 to the TMS24. The TMS 24 pays out and takes up a tether 28 that extends betweenthe TMS 24 and the ROV 10. The umbilical 26 and tether 28 communicatepower, e.g., electrical power, and data between the control interface 12and the TMS 24 and ROV 10. The data communicated on the umbilical 26 andtether 28 includes control signals to actuators of the TMS 24 and ROV 10and other control communications, output from sensors at the TMS 24 andROV 10, and other data.

The ROV 10, in turn, supplies power, e.g., electrical and/or hydraulicpower, and exchanges data with the tool 18 through the manipulator arm16, enabling the operator to actuate and operate the tool 18 via thecontrol interface 12. The tool 18 and ROV 10 communicate data includingcontrol signals to actuators in the tool 18, output from sensors in thetool 18, and other data, via the manipulator arm 16, which, in turn, canbe communicated with the control interface 12.

FIG. 1 shows the tool 18 as a jaws with two parts that can be operatedto open and close to grasp and hold objects. But, there are a multitudeof different tools that can be used with an ROV, including torque tools,cutters and other tools. A tool interchange 20 mounts at the end of themanipulator arm 16, between the manipulator arm 16 and the tool 18,becoming the interface between the arm 16 and the tool 18. The toolinterchange 20 enables the ROV 10 to change out tools 18 while subseawith no outside assistance. While there are many examples of toolinterchange 20 that could be used herein, co-pending U.S. applicationSer. No. 16/376,622, filed Apr. 5, 2019 and entitled “Submersible RemoteOperated Vehicle Tool Interchange,” shows an example tool interchange 20that can be used herein.

As discussed in more detail below, the operator can operate themanipulator arm 16 to dock into a tool holder of a tool storage unit 32.The operator can then actuate the tool interchange 20 to release thetool from the manipulator arm 16, withdraw the manipulator arm 16 fromthe tool holder of the tool storage unit 32 and leave the tool 18 in thetool storage unit—in other words, stow the tool 18. The operator canthen operate the manipulator arm 16 to dock in a different tool holderstoring a different tool 18, and actuate the tool interchange 20 to lockto and establish data and power communications with the different tool18—in other words, connect to a tool 18. Thereafter, the operator canwithdraw the manipulator arm 16 from the tool holder and use thedifferent tool 18 in performing operations. The tool storage unit 32 maybe on the ROV 10, on the TMS 24, in both locations and/or elsewhere. Thetool storage unit 32 may be a fixed tool storage unit (i.e., with one ormore tool holders fixed in position) or a changeable type (i.e., withmultiple tool holders, each moveable to be selectively presented forconnecting to or stowing a tool). In certain instances of the toolstorage unit 32 being a changeable type, the operator can use thecontrol interface 12 to select a particular tool or tool holder from amenu, and the tool storage unit 32 will operate to move the tool holdersto present the tool holder to allow the manipulator arm 16 to connect toor stow a tool. In certain instances, the tool storage unit 32 is acarousel type, where the tool holders are arranged on a disk thatrotates on its central axis to selectively align the tool holders to bepresented.

FIG. 2 is a perspective view of an example tool holder 200 that can beused in the tool storage unit 32 described above. The example toolholder 200 is shown with a docked manipulator arm, and morespecifically, shown receiving a tool 18 locked to a tool interchange 20.The remainder of the manipulator arm 16 has been omitted for clarity ofillustration, but would extend outward from the back of the toolinterchange 20 (similar to that shown in FIG. 1 ). The tool holder 200includes a housing 202, shown here as a frame, with a face plate 204.The housing 202 defines a receptacle 206 that receives and holds thetool 18, so that the tool can be stored when not in use.

The face plate 204, better shown in the perspective view of FIGS. 3A and3B, has an opening 208 sized to pass the tool 18. A plurality of lead-inramps 210 are positioned surrounding the opening 208. In FIG. 3A, threelead-in ramps 210 are shown, equally distributed around the opening 208,but fewer or additional lead-in ramps 210 could be provided. Also, FIG.2 shows the lead-in ramps 210 formed on a common ring affixed to thefront surface of the face plate 204, while FIG. 3A shows discretelead-in ramps 210, separately affixed to the front surface of the plate204. The lead-in ramps 210 each have a ramped inward facing surface 212,and the surfaces 212 of the lead-in ramps 210 cooperate with one anotherto define a generally conical guide, decreasing in diameter toward theopening 208. Accordingly, the lead-in ramps 210 are able to contact theouter periphery of a tool 18 received at the mouth of the lead-in ramps210 and guide the tool 18 in position and orientation toward and throughthe opening 208 and into the receptacle 206 as the tool 18 is movedtoward and into the receptacle 206. The face plate 204 also includesfeatures to lock the tool in place. In certain instances, the featurescan be provided on the lead-in ramps 210 (or the ring at the base of thelead-in ramps 210 as in FIG. 2 ) in the form of a twist-lock keyway 224that engages corresponding key 226 on the periphery of the tool 18. Whenthe keys 226 of the tool 18 are received in the keyways 224, and thetool 18 rotated (clockwise in FIG. 3B), the keys 226 lock into thekeyways 224, eventually bottom out at the end of the keyways 224, andsignal to the ROV or operator that the tool 18 is fully received, lockedand rotationally aligned in the tool holder 200. The key/keyways alsoaxially align and support the tool 18 in the tool holder 200. In certaininstances, the key/keyways can be reversed, having keys carried on theface plate 204 and a keyway on the tool 18.

The face plate 204 also has a visual tag 214 that includes an alignmentfiducial 216 and a tool location identification marking 218. In certaininstances, the alignment fiducial 216 can be embedded within the toollocation marking 218 as shown, or it can be separate from the toollocation identification marking 218. The alignment fiducial 216 is in aspecified position and orientation relative to the opening 208 andreceptacle 206 of the tool holder 200, so that it can be used (asdiscussed below) in guiding the manipulator arm to dock. In certaininstances, the alignment fiducial 216 is of a type for 2D positionlocation. In certain instances, the tool location marking 218 caninclude a human readable marking identifying the tool 18 specified to bestored in the associated receptacle 206 and/or a machine readablemarking, like a barcode, quick response “QR” code, or another type ofmachine readable marking, identifying the tool location.

A camera 220 is carried on the manipulator arm, shown in FIG. 2 as beingmounted directly to the tool interchange 20 (that, in turn, is mounteddirectly to the manipulator arm). In other instances, the camera 220could be mounted directly to the arm itself or to another componentcarried by the arm to enable the camera 220 clear sight of the visualtag 214 as the tool 18 is being docked. In certain instances, the camera220 can be carried by the tool storage unit or something else (e.g., theTMS or other device carrying the tool storage unit). For example, ininstances where the tool storage unit is remote from the ROV, the camera220 might be mounted remote from the ROV.

FIG. 3B shows the tool 18 as it would be positioned when stowed in thetool holder 200, but with the remainder of the tool holder 200 omittedfor clarity of illustration. When stowed, a male mount 222 of the tool18 protrudes through the opening 208 of the face plate 204. The malemount 222 is received in a corresponding receptacle of the toolinterchange 20 on the manipulator arm 16, and the tool interchange 20grips the male mount 222 to lock the tool 18 to the manipulator arm 16.In certain instances, the male mount 222 includes alignment features tocenter the tool interchange 20 to the tool 18 and rotationally align thetool interchange 20 to the tool 18. For example, in certain instances,the male mount 222 is generally frusta-conical which centers in acorresponding frusta-conical shape of the tool interchange 20 to centerthe tool 18 to the tool interchange 20, and position the tool 18 in aspecified location relative to the manipulator arm 16. Rotationalalignment, for example, can be achieved by a key and keyway on the malemount 222 and tool interchange, in certain instances.

The concepts herein encompass a system for control of the TMS 24 and ROV10 (including the manipulator arm 16 and tool 18) by computer, having aprocessor 402 with memory 404, that receives input from sensors 414 ofthe TMS and/or the ROV and signals actuators 416 that operate the TMS 24and/or the ROV 10. In particular, the memory 404 stores instructionsthat cause the processor 402 to perform the operations described herein.The actuators 416 include actuators at each of the joints (e.g., joints22, FIG. 1 ) that move the joints in moving the manipulator arm, as wellas other actuators. The sensors 414 include one or more positionsensors, force sensors (linear and/or torque), the camera (e.g., camera220), as well as other sensors. In certain instances, the sensorsinclude a sensor in the manipulator arm, near the tool interface,capable of sensing force and/or torques in 6 degrees of freedom. Incertain instances, the sensors include a force (liner and/or torque),pressure and/or position sensor at each of the joints (e.g., joints 22)of the manipulator arm. The processor 402 could be a single processor ormultiple processors in communication with each other, and the memory 404could be a single memory or multiple memories in communication with eachother. FIG. 4 schematically shows an example of the control interface12, and for convenience of reference, processor 402 and memory 404 aredepicted within a housing 406 of the interface 12. Although shown as allwithin the housing 406, processor 402 could be distributed, with aspectsremote from the housing 406. In certain instances, all or some of thememory 404 could be embedded in a processor. Likewise, although thememory 404 is depicted as one memory, it could be multiple memories allwithin the housing 406 or with one or more of the memories distributed,remote from the housing 406. In certain instances, the processor 402 isa system of processors distributed in the manipulator arm, ROV and/orhousing 406 each with associated (embedded or separate) memory. Theprocessor 402 and memory 404 are in communication with the sensors ofthe system.

The control interface 12 includes a display 408 and a user input 410through which the human operator interfaces with the control interface12. The display 408 can include one or multiple screens, goggles and/orother types of displays. The user input 410 can include one or multipletypes of user input, such as keyboards, hand controllers, physicalbuttons and switches and/or other types of user inputs. The controlinterface 12 can present the human operator with information about theoperation of the ROV, TMS and the environment, as well as menus ofoptions for controlling the system, such as soft menus 412 as depictedin FIG. 4 displayed via the display 408.

In operation, the human operator commands operation of the ROV 10,including the manipulator arm 16 and any connected tool 18, and the TMS24 via the control interface 12. Beyond controlling the ROV 10 to flyaround and controlling the manipulator arm 16 and tool 18 in performingoperations, the operator can effectuate docking the arm 16 to a toolholder, such as tool holder 200 (FIG. 2 ), of a tool storage unit 32.The system described herein automates the docking, which can beactivated via the control interface 12 (e.g., via a menu 412, the input410 and/or other manner).

FIG. 5 is a flow chart of example method steps in automated docking ofthe manipulator arm (with or without an attached tool) to a tool holder.In certain instances, before the automation begins, the operatoroperates the arm to an initial or ready position in proximity to thetool holder. For example, when the tool holder is apart from the ROV,the operator flys the ROV to the tool holder and operates the arm to aposition near the tool holder. When the tool holder is on the ROV, theoperator positions the arm so it is free of external obstructions andable to move to the tool holder. In response to a command to activatethe automated docking, the automated docking sequence is initiated, atoperation 502, by determining a nominal path between the current orready position and orientation of the arm and a docked position andorientation with the arm docked to the tool holder. Throughout operationof the arm, both before and after activation of the automated docking,the system receives and logs input from sensors in the arm and thusknows the current position and orientation of the tool, the joints, andthe arm, overall, in 6 degrees of freedom. When the tool storage unit iscarried on the ROV, the system likewise knows the position andorientation of the tool holder in 6 degrees of freedom and can, in turn,automatically (i.e., without human assistance) calculate the nominalpath of the arm to dock to the tool holder. In calculating the nominalpath, the system operates a kinematic model of the manipulator arm anduses this model to calculate the movement of the joints necessary tomove the tool into proximity of the opening in the tool holder and todock with the tool holder, i.e., position and orient the arm so the armcan be connected to a tool protruding from the opening or a tool on thearm inserted into the receptacle of the tool holder. When the toolstorage unit is carried apart from the ROV, such as on the TMS, theoperator flies the ROV to the tool holder and operates the arm intoproximity to the tool holder so the camera can see the tool holder. Oncethe camera is able to see the tool holder, and the system recognizes theposition and orientation of the tool holder, the system canautomatically calculate and adjusts the nominal path of the manipulatorarm from its current position and orientation to the position andorientation corresponding to the arm docked with the tool holder. Incertain instances, the system identifies the alignment fiducial on thetool holder and uses the alignment fiducial in recognizing the toolholder position and orientation.

At operation 504, the system implements movement of the manipulator armalong the nominal path by signaling the actuators at the joints of themanipulator arm to move according to the determined nominal path. Incertain instances, the movement can be fully automatic, with no inputfrom the human operator. In other instances, the movement can becontrolled to some degree by the human operator. For example, in certaininstances, the human operator, using the control interface, can controlthe speed and start/stop the movement of the arm while the arm isautomatically guided along the nominal path.

At operation 506, the system can implement one or more control loopstaking feedback from sensors in iteratively controlling the path of thearm (with or without tool) from the nominal path to account fordiscrepancies between the nominal path and the actual path needed todock the arm to the tool holder (operation 508). In certain instances,operation 506 can be implemented using images (still or video) from thecamera, and in certain instances other sensors (e.g. position sensors atthe joints and/or other sensors), as feedback to iteratively makecorrections to the manipulator arm path. This control loop is discussedin more detail with respect to FIG. 6 . In certain instances, operation506 can be implemented using output from the one or more force sensorsof the manipulator arm that register forces exerted by the arm on theenvironment, and in certain instances other sensors (e.g., positionsensors at the joints and/or other sensors), as feedback to iterativelymake corrections to the manipulator arm path. This force accommodationcontrol loop is discussed in more detail with respect to FIG. 7 . Incertain instances, both the image feedback and force accommodation canbe used in nested control loops and/or the control corrections of eachrelatively weighted (e.g., with the image feedback having greater orlesser influence on the determined corrections than the force sensorfeedback) in iteratively correcting the manipulator arm path.

Referring to FIG. 6 , in operation of the image feedback loop, thecamera takes an image of the tool holder at operation 602. At operation604, the image is analyzed to identify the position and orientation ofthe tool holder. In certain instances, the image is analyzed to identifythe position and orientation of the tool holder using alignmentfiducial. Thereafter, a pose estimation calculation is performed. Theimage of the tool holder, and in certain instances the alignmentfiducial, is compared to a specified location relative to the camera tocalculate the position and orientation of the tool holder to the camera.At operation 606, the system, in turn, determines the position andorientation of the tool holder relative to the manipulator arm, based ona specified relationship between characteristics in tool holder image,e.g., the alignment fiducial and/or other characteristics, and aspecified relationship between the camera and the manipulator arm. Atoperation 608, the system calculates whether the manipulator arm ispositioned and oriented to successfully dock based on the current path.If not, it calculates corrections from the current path to a newspecified path that (at least based on the current data) positions andorients the arm to successfully dock to the tool holder, and sends newsignals to the actuators at the joints to effectuate the new specifiedpositions and orientations. In certain instances, the system canadditionally or alternately operate other aspects of the ROV, such asthe thrusters used to navigate the ROV in the water, to adjust theposition and orientation of the arm to successfully dock to the toolholder. Operating the thrusters to reposition the ROV, for example, maybe helpful in instances where the tool storage unit is separate from theROV (e.g., on the TMS or elsewhere). Finally, at operation 610, themanipulator arm moves to the new specified positions and orientations.The feedback loop begins again at operation 602 and repeats, updatingthe manipulator path position and orientation, until the manipulator armis successfully docked on the tool holder (e.g., as shown in FIG. 2 ).

Referring to FIG. 7 , in operation of the force accommodation loop, theone or more force sensors measure forces (linear and/or torque) exertedby the manipulator arm on the environment at operation 702. For example,when the manipulator arm or tool contacts one or more of the lead-inramps of the tool holder, the force sensors measure the resultant forcesin the 6 degrees of freedom.

Based on this sensor input, the system determines whether the force inany of the 6 degrees exceeds a specified threshold. If it is determinedthat the measured force in any of the 6 degrees exceeds thecorresponding specified threshold, at operation 704, the systemcalculates movements of the manipulator arm (in 6 degrees of freedom) toreduce the force below the exceeded specified threshold or thresholdsand signals the actuators at the joints to effectuate the movement. Incertain instances, there can be different specified thresholds for someor all of the 6 degrees of freedom. For example, as the manipulator armis extended forward, toward the tool holder and tool holder receptacle,the ramped surfaces of the lead-in ramps drive the arm laterally toorient and center the arm on the opening in the tool holder and the toolreceptacle. Thus, by having a lower specified threshold in the degree ordegrees of movement that correspond to these imposed lateral forces thanthe specified threshold in the degree of movement corresponding to theforward extension direction, the system accommodates the mechanicalalignment imposed by the lead-in ramps. In certain instances, if theforward extension corresponds to the Y-axis, the specified threshold forY-axis is greater than the specified threshold for the X-axis, Z-axis,pitch and yaw. In certain instances, the force accommodation can beimplemented as a stiffness control, an impedance control, an admittancecontrol or another type of control. For example, in certain instancesthe force control can be a hybrid position/force control thatprioritizes force control for specified degrees of freedom over positioncontrol for those degrees of freedom and vice versa. Moreover, theposition control, including control to a nominal path and/or imagefeedback discussed above, can be operated as either an inner controlloop to the force accommodation control loop or operated as an outercontrol loop to the force accommodation control loop, where the innercontrol loop would have a faster loop rate and have priority over theouter control loop. For example, in certain instances, an admittancecontrol force accommodation loop has position feedback loop as an innerloop. In another example, in certain instances, an impedance controlforce accommodation is the inner loop with position feedback as theouter loop.

At operation 708, the manipulator arm moves per the movements signaledin operation 706. The feedback loop begins again at operation 702 andrepeats, updating the manipulator path position and orientation, untilthe manipulator arm is successfully docked on the tool holder (e.g., asshown in FIG. 2 ).

Referring back to FIG. 5 , once the manipulator arm is docked, atoperation 510, in certain instances, if the manipulator arm is without atool, the tool interface can be manually (e.g., by the human operator)or automatically actuated to connect to a tool in the tool holder. Incertain instances, if the manipulator arm is connected to a tool, thetool interface can be manually or automatically actuated to release andstow the tool in the tool holder.

Thereafter, the manipulator arm can be withdrawn and moved back to the(same or different) ready position, for example, by automaticallydetermining a nominal path to the ready position at operation 512. Atoperation 514, the system implements movement of the manipulator armalong the nominal path by signaling the actuators at the joints of themanipulator arm to move according to the determined nominal path. Asdiscussed above, in certain instances, the movement can be fullyautomatic, with no input from the human operator. In other instances,the movement can be controlled to some degree by the human operator. Atoperation 516, as discussed above (operation 506), the system canimplement one or more control loops taking feedback from sensors initeratively controlling the path of the arm (with or without tool) fromthe nominal path to account for discrepancies between the nominal pathand the actual path needed to position the arm in the ready position.Finally, the process is complete at operation 518, when the arm has beenmoved to the ready position.

The process of FIG. 5 can be performed again to dock to a different toolholder and acquire/stow a different tool.

In certain instance, automating docking of the manipulator arm to thetool holder can speed up the process of changing or stowing tools. Forexample, wholly manually controlling the manipulator arm to dock to thetool holder is a difficult process, requiring a high level of operatorskill and takes even a highly skilled ROV operator tens of minutes tocomplete. In certain instances, automated docking can be completedwithin a minute or a few minutes. The time saved translates directly tocosts saved as, not only is the ROV's work performed more quickly, butother work need not wait as long on the ROV's work. Automated docking ofthe arm to the tool in the holder can also reduce the required operatorskill level.

While a number of implementations have been described, it should beappreciated that the concepts herein are not limited to thoseimplementations. Rather, other changes, substitutions, and alterationsare also possible without departing from this disclosure.

We claim:
 1. A method, comprising: receiving data from a submersibleremote operated vehicle (ROV) about the operation of an arm of the ROV;automatically controlling, based on the data, movement of the armrelative to a target; where receiving data comprises receiving data froma camera, the data comprising an image of an alignment fiducialassociated with the target; and where automatically controlling movementof the arm comprises automatically controlling the movement of the armto align the arm relative to the target.
 2. The method of claim 1, whereautomatically controlling movement of the arm relative to a target,comprises automatically controlling movement of the arm in docking thearm to a tool holder, where the tool holder is the target.
 3. The methodof claim 2, where docking the arm to the tool holder comprises insertinga tool on the arm into the tool holder; and comprising releasing thetool from the arm.
 4. A method comprising: receiving data from asubmersible remote operated vehicle (ROV) about the operation of an armof the ROV; automatically controlling, based on the data, movement ofthe arm relative to a target; where automatically controlling movementof the arm relative to the target, comprises automatically controllingmovement of the arm in docking the arm to a tool holder, where the toolholder is the target; receiving an input from a human operatoridentifying a tool; and in response to the input operating a toolcarousel to present the tool holder containing the tool to an accessposition.
 5. The method of claim 1, where aligning the arm relative tothe target comprises aligning a device coupled to the arm relative tothe target.
 6. The method of claim 5, where the device comprises a tool.7. A method comprising receiving data from a submersible remote operatedvehicle (ROV) about the operation of an arm of the ROV; andautomatically controlling, based on the data, movement of the armrelative to a target; where receiving data comprises receiving data froma force sensor of the arm; and where automatically controlling movementof the arm comprises automatically controlling movement of the arm basedon a force threshold and an automatically determined nominal path to thetarget.
 8. The method of claim 7, where the force sensor comprises atorque sensor; and where automatically controlling movement of the armcomprises automatically controlling movement of the arm based on atorque threshold and an automatically determined nominal path to thetarget.
 9. The method of claim 7, where automatically controllingmovement of the arm further comprises automatically controlling movementof the arm based on a second, different force threshold in a differentdirection than the first mentioned force threshold.
 10. The method ofclaim 9, where the first mentioned threshold is in an extensiondirection of the arm and the second force threshold is lateral to theextension direction, and where the first mentioned threshold is greaterthan the second threshold.
 11. The method of claim 7, where receivingdata comprises receiving data from a camera, the data comprising animage of the target; and where automatically controlling movement of thearm further comprises automatically controlling the movement of the armbased on the image to align the arm relative to the target.
 12. Themethod of claim 1, comprising repeatedly receiving arm movement inputfrom a human operator during the automatically controlling.
 13. A systemcomprising a processor and memory with instruction stored on the memoryoperable to cause the system to perform operations comprising: receivedata from a submersible ROV about the operation of an arm of the ROV;automatically control, based on the data, movement of the arm relativeto a target where receiving data comprises receiving data from a camera,the data comprising an image of an alignment fiducial associated withthe target; and where automatically controlling movement of the armcomprises automatically controlling the movement of the arm to align thearm relative to the target.
 14. The system of claim 13, whereautomatically controlling comprises automatically controlling, based onthe data, movement of the arm in docking the arm to a tool holder. 15.The system of claim 13, where receiving data comprises receiving datafrom a force sensor of the arm; and where automatically controllingmovement of the arm comprises automatically controlling movement of thearm based on a force threshold and an automatically determined nominalpath to the target.
 16. The system of claim 15, where receiving datacomprises receiving data from a camera, the data comprising an image ofthe target; and where automatically controlling movement of the armfurther comprises automatically controlling the movement of the armbased on the image to align the arm relative to the target.
 17. Thesystem of claim 15, where automatically controlling movement of the armfurther comprises automatically controlling movement of the arm based ona second, different force threshold in a different direction than thefirst mentioned force threshold.
 18. The system of claim 17, where thefirst mentioned threshold is in an extension direction of the arm andthe second force threshold is lateral to the extension direction, andwhere the first mentioned threshold is greater than the secondthreshold.
 19. A submersible ROV system, comprising: a submersible ROVwith a manipulator arm for carrying a tool; a tool holder for storingthe tool; a control system configured to receive data from sensors ofthe ROV about the operation of the arm and automatically control, basedon the data, movement of the arm in docking the arm to the tool holder;where receiving data comprises receiving data from a camera, the datacomprising an image of an alignment fiducial associated with the target;and where automatically controlling movement of the arm comprisesautomatically controlling the movement of the arm to align the armrelative to the target.
 20. The submersible ROV system of claim 19,where the tool holder is carried by the ROV.
 21. The submersible ROVsystem of claim 19, where the sensors comprise a camera; and where thecontrol system is configured to receive image data from the camera. 22.The submersible ROV system of claim 19, where the sensors comprise aforce sensor configured to sense forces exerted by the manipulator arm;and where the control system is configured to receive force data fromthe sensor.
 23. The submersible ROV system of claim 19, where the toolholder comprises: an opening through which the tool is passed whendocking the arm to the tool holder; and a conical guide, surrounding theopening and decreasing in diameter toward the opening.
 24. Thesubmersible ROV system of claim 23, where the conical guide comprises aplurality of lead-in ramps, each having a ramped inward facing surface.25. A submersible ROV system, comprising: a submersible ROV with amanipulator arm for carrying a tool; a tool holder for storing the tool;a control system configured to receive data from sensors of the ROVabout the operation of the arm and automatically control, based on thedata, movement of the arm in docking the arm to the tool holder; and akey or keyway on the tool holder configured to interface with acorresponding keyway or key on the tool and lock the tool to the toolholder.